1. Field of the Invention
The present invention relates to a mounting structure for a measuring device which measures the dimension of a ground portion for performing a grinding while controlling the dimension of the ground portion. Particularly, it relates to a mounting structure for a measuring device which is designed for use in a cylindrical grinding machine. Further, the present invention relates to a grinding machine with the mounting structure.
2. Discussion of the Related Art
Cylindrical grinding machines generally take the construction that a bed has mounted thereon a work head having a work spindle for rotatably supporting and driving a workpiece and a wheel head having a rotating grinding wheel and that the work head and the wheel head are relatively moved in a Z-direction parallel to the rotational axis of the work spindle and an X-direction perpendicular thereto to grind the workpiece. Such cylindrical grinding machines are classified into a table traverse type that the grinding operation is performed by moving a table with the work head fixed thereon on the bed in the Z-direction and by moving the wheel head on the bed in the X-direction and a wheel head traverse type that the grinding operation is performed by moving the wheel head relative to the work head fixed on the bed in two directions of Z and X. The table traverse type has heretofore been the mainstream of cylindrical grinding machines, wherein the length of the machine in the Z-direction becomes long because a table elongated in the Z-direction is moved in the Z-direction. However, these days the wheel head traverse type is becoming the mainstream of cylindrical grinding machines because of an increasing demand for the downsizing of the machines. In the wheel head traverse type, it is general to take the construction that the wheel head is mounted movably in the X-direction on a slide base which is mounted movably on the bed in the Z-direction.
In the table traverse type, on the contrary, it is ordinary to mount a measuring device on a pillar upstanding at a front portion of the bed which is adjacent to the grinding wheel in the Z-direction and which is on the side opposite to the grinding wheel in the X-direction. With this construction taken, it does not occur that the grinding wheel and the measuring device are moved relatively in the Z-direction even when the workpiece is moved relative to the grinding wheel in the Z-direction. Therefore, any ground portion on the workpiece can be measured at all times by the measuring device remaining in front of the grinding wheel, so that a mounting structure for the measuring device can be simplified. By the way, in cylindrical grinding machines, an opening which can be selectively opened for the loading/unloading of the workpiece as well as for the maintenance of attachments provided in a grinding area is provided at a front part of a cover for preventing coolant supplied to the grinding area from splashing. In the aforementioned mounting structure for the measuring device, since the same is arranged around the opening portion of the cover, there arises a problem in that the mounting structure becomes an obstacle in performing the loading/unloading of the workpiece and the maintenance of the attachments. For the purpose of solving the problem, it has been practiced to arrange the measuring device at an end part of the opening portion or at a part being within the cover but being deviated from the opening portion, in which case a resultant problem arises in that the adjustment and maintenance of the measuring device per se becomes difficult to perform.
In the wheel head traverse type, on the other hand, it is first conceivable to mount the measuring device on the bed. With this structure taken, the measuring device cannot be moved relative to the workpiece, and thus, where grinding operations are to be performed on ground portions of a workpiece which are spaced at plural places in the Z-direction, measuring devices for the respective ground portions have to be provided, resulting in an increase in the facility cost. Further, where workpieces respectively having ground portions at different positions in the Z-direction are to be ground in succession, there arises an inconvenience that the position of the measuring device has to be changed each time of one grinding operation. Further, like the table traverse type as aforementioned, there arises a problem that the measuring device positioned at the opening portion of the cover makes an obstacle against the maintenance and adjustment of various attachments therearound. As a measure for solving these problems, there have been known a structure that a measuring device is mounted movably in the Z-direction on a bed or a member such as a table mounting a work head thereon and another structure that a measuring device is mounted on a wheel head.
The structure that the measuring device is mounted movably in the Z-direction is disclosed in Japanese Utility Model No. 2601057 for example. In the know structure, as shown in FIGS. 1 to 3 of the Japanese Utility Model, a slide table 6 is mounted movably in the axial direction of a work spindle 3a on a table 2, which mounts thereon a work head 3 and a foot stock 4 for supporting a workpiece W, on a side opposite to the side where the machining of the workpiece W is performed, and the slide table 6 is provided with a servomotor 11 driven in response to a signal designating the workpiece or a measuring position on the workpiece W and a conversion mechanism 14-19 for converting the rotation of the servomotor 11 into the reciprocating movement of the slide table 6, wherein a measuring device main body 10 is secured on the slide table 6. With this structure, it can be realized to automatically move the measuring device main body 10 to any programmed measuring position on the workpiece W, and it becomes possible to evacuate the measuring device main body 10 to a suitable position where the measuring device main body 10 does not interfere with the loading/unloading of the workpiece and the maintenance for attachments provided in the grinding area.
Further, the structure for mounting the measuring device on the wheel head is disclosed in Japanese Unexamined, Published Patent Application No. 2000-127038. As shown in FIGS. 1 and 2 of the Japanese Application, the application relates to a grinding machine with twin wheel heads 8, 9, wherein measuring devices 20 are mounted on the top surfaces of the respective wheel heads 8, 9. More specifically, each wheel head mounts a support member 21 for the measuring device 20 on the top surface thereof, a second arm 23 is pivotably carried at an extreme end of a first arm 22 which is pivotably carried by the support member 21 to extend forward, and a measuring rod 28 for measuring dimensions is secured approximately at right angles to an extreme end of the second arm 23. The measuring rod 28 is composed of a V-block 25 secured at an extreme end thereof and contactable with the outer surface of a crankpin CP to be machined and a probe 27 provided at the center part of the V-block 25 to be movable back and forth and electrically detects the back and forth movement of the probe 27 to output the detected movement as an electric signal. The measuring device 20 is provided with an actuator or hydraulic cylinder 31 for moving the measuring rod 28 selectively to a parked position and a measuring position. In the measuring device 20, the hydraulic cylinder 31 turns the first arm 22 upward to hold the measuring rod 28 at the parked position as indicated by the phantom line in FIG. 2 of the Japanese application, in which state the second arm 23 pivotable about the extreme end of the first arm 22 would not be held at a fixed position. With this taken into account, a third arm 24 is secured to the extreme end of the first arm 22 to extend downward, and a support protrusion 29 at the extreme end of the third arm 24 holds the second arm 23 at the fixed position while the measuring device 20 is at the parked position. The measuring device 20 needs a complicated link mechanism as aforementioned for the purpose of holding the V-block 25 and the probe 27 in contact with the outer surface of the crankpin CP to be ground, in a predetermined relation even though the wheel head 9 is moved in the X-direction during each grinding operation.
As described above, in the wheel head traverse type, the structure that mounts the measuring device on the member supporting the work head, to be movable in the Z-direction requires the slide table, the servomotor for operating the same and the conversion mechanism for converting the motor rotation into the reciprocating movement of the slide table and thus, unavoidably results in a substantial increase in the facility cost. Further, in the wheel head traverse type, the structure that mounts the measuring device on the wheel head requires the complicated link mechanism as aforementioned and thus, also unavoidably results in an increase in the facility cost. In addition, the link mechanism needs considerable rigidity for higher measuring accuracy of the measuring device and is increased also in weight. Because this results in further increasing the weight exerted on the top surface of the wheel head which is supported to be movable in the X-direction on the slide base which is in turn supported on the bed to be movable in the Z-direction, there is a risk of deteriorating the feed accuracy and the positioning accuracy of the wheel head. Further, the addition of the large weight mechanism to a high position may have a risk of generating chattering vibration. Furthermore, since electric wires and hydraulic conduits for the measuring device suffer bending and stretching in two directions of Z and X, there arises an additional problem involving a risk of breaking or damaging the electric wires and the hydraulic conduits.